This invention relates to diesel engine testing and, more particularly, to a method and apparatus for testing for combustion gas leakage caused by broken or cracked pistons or damaged piston rings.
Diesel engines for use in high horsepower applications such as, for example, diesel electric propulsion systems for locomotives or ocean-going ships, are heavy duty units with few user serviceable components. The cylinders of such engines often include a steel liner welded to a steel head. Since major disassembly is required to open such a cylinder for inspection, it is desirable to provide test equipment that can detect a failure mode within a cylinder without such disassembly.
One exemplary failure in diesel engine cylinders results from combustion gas leakage from the cylinder into the engine crankcase. Not only does such leakage detrimentally affect engine efficiency but it also undesirably pressurizes the engine crankcase. While compression testing is often used for detecting cylinder leakage, such testing can be adversely affected by weak batteries and engine temperature, and some leakage problems can be masked by compression testing. Further, compression testing is time consuming compared to leakage testing. One method of leakage detection has been to pressurize a cylinder with air and then observe the time required for the pressure to drop to some preselected low value. This prior method generally uses "shop air" which may be at varying pressure, and relies more on "feel" rather than precise measurement. For example, shop personnel generally count off a number of seconds rather than use a timer to accurately measure time duration. However, since air pressure is a variable, some variation in the measured time duration has been acceptable. In general, this prior method will identify gross failures while slow leaks that may result from an incipient failure mode will be missed. Accordingly, it is desirable to provide a method and apparatus for more accurately measuring cylinder leakage for identifying piston and piston ring failures.